A pipe pig is a vessel that travels along the bore of a pipeline, such as an oil pipeline. Pipe pigs are often propelled along the pipeline by fluid (e.g. oil) flowing within the pipeline. So-called inspection pipe pigs often include sensors for collecting data about the pipeline as the pipe pig travels along the pipe and may be used to inspect the condition of the pipe walls.
An example of a typical inspection pig is described in US-A-2007022830 which makes use of magnetic flux sensors for collecting data. The sensors are mounted on moveable arms that extend from a rigid body, where the moveable arms ride against the internal profile of the pipeline as the inspection pig travels through the pipe.
Inspection pigs are often long, heavy and expensive pieces of apparatus that require a specialist launching station for inserting the pig into the pipeline and a specialist receiving station for retrieving the pig from the pipeline. As such, the preparation, travel and retrieval of an inspection pipe pig through a pipeline is an expensive, time-consuming and disruptive process. Furthermore, inspection pigs are known for being liable to get stuck within a pipeline and this often results in the pipeline being shutdown until the stuck inspection pig is removed. For certain pipelines (e.g. oil pipelines), any shutdown can be significantly costly. Inspection pigs are often sized for a specific diameter pipeline and have limited ability in negotiating bends in the pipeline or moving between areas of the pipeline with differing diameters. Therefore, a given inspection pig may only be used with pipelines having a suitable specification and multiple inspection pigs are required for inspection of wider ranges of pipelines.
It is an object of certain embodiments of the present invention to provide an improved pipe pig that overcomes at least some of the disadvantages associated with the prior art.